Tc 9-524 fundamentals of machine tools

POWER HACKSAWING
Power hacksawing machines cut by drawing the hacksaw
blade toward the motor end of the machine.
At the
completion of this movement called the draw stroke, the
hacksaw blade is lifted slightly to clear the material being cut
and moved an equal distance in the opposite direction.
Mounting Workpieces
Workpieces for metalcutting machines are not mounted to
the machine, but are supported by the table of the machine and
guided by one of the sawing machine attachments or by hand.
Power Hacksaw Speeds.
Since the cutting speed of hacksawing machines is measured
in strokes per minuet, the length of the stroke is an important
consideration. A longer stroke at a given speed will cut faster
than a shorter stroke at the same speed. Thus. to obtain a
proper cutting speed the length of the stroke must be
specified.
The length of the stroke of most power hacksaws is between
4 and 10 inches depending upon the size of the machine. On
machines with an adjustable stroke, the wider the stock being
cut, the shorter the stroke to prevent the blade holders from
hitting the stock.
With most power hacksaws, the stroke length is adjustable
within 2 or 3 inches. and on some machines more than one
speed can be selected. On single-speed hacksawing machines,
the speed must be regulated by changing the stroke.
6-11

---

TC 9-524
If the stroke is doubled the machine will cut twice as fast,
and if the stroke is decreased by one-half, the machine will cut
half as fast. This proportion can be applied to any fraction to
increase or decrease the cutting speed of the machine.
The speeds given in the chart, Figure 6-16, bellow are for
example only. The correct speeds for cutting various metals
will depend on the type of machine you are using. In general
the faster speeds are used for cutting soft materials and the
slower speeds are used for cutting harder materials. If a
recommended speed cannot be approximated either by
changing the stroke or changing the speed, the feed can be
decreased to prevent undue wear to the hacksaw blade.
Power hacksaw machines having a mechanical feed can
usually be regulated to feed the saw downward from 0.001 to
0.025 inch per stroke, depending upon the type and size of the
material to be cut. On these machines, a device to stop the
feed when hard spots are encountered is usually incorporated
The feed of machines having gravity feed is regulated by the
weight of the saw frame and any additional weights or springs
that might be connected or attached to the frame to increase or
decrease the downward force of the hacksaw blade.
Maximum and minimum blade pressures obtainable are
determined by the manufacturer of the hacksawing machine,
and are specified as relatively light or heavy.
The following general rules apply for selecting proper feeds
for hacksawing machines:
The feed should be very light when starting a cut and can
be increased after the cut is well started.
Hard materials require a lighter feed than soft materials;
reduce the feed when welds or hard spots in materials are
encountered.
Wide material requires a heavier feed than narrow
material because the pressure is distributed over a larger
into the design.
surface.
Sharp hacksaw blades will cut well with lighter feeds.
Heavier feeds are necessary for cutting with dull blades.